Plastic lenses are lighter than inorganic lenses, are not easily broken, and are dyeable. Therefore, they have been rapidly become widespread and are used for optical elements such as spectacle lenses and camera lenses. Up to now, various resins for lenses have been developed and used, and typical examples thereof include a thiourethane resin obtained from a polymerizable composition which contains an isocyanate compound and a thiol compound.
For example, the following Patent Documents 1 to 5 relate to plastic lenses comprised of the thiourethane resin.
Patent Documents 1 and 2 disclose a polymerizable composition obtained by mixing a prepolymer, which is obtained by reacting sulfur with an epithio group-containing compound by using an imidazole-based catalyst as a vulcanization accelerator, with a polyisocyanate compound and a polythiol compound, and a plastic lens obtained from the composition.
Patent Document 3 discloses a photosensitive resin composition containing a thiourethane compound, which is obtained from a thiol compound and an isocyanate compound, and a photopolymerization initiator such as an imidazole compound.
Patent Document 4 discloses a process for producing a polythiourethane resin in which a polythiol oligomer is reacted with a poly(thio)isocyanate group-containing compound. According to the document, the polythiol oligomer is obtained by reacting a polythiol compound having two or more functional groups with sulfur by using an imidazole-based catalyst.
Patent Document 5 discloses a polymerizable composition containing (A) a compound having one or more mercapto groups, (B1) a polyurethane prepolymer and/or a polythiourethane prepolymer having terminals totally or partially composed of a mercapto group, and (C) a polyisocyanate compound and/or a polyisothiocyanate compound. According to the document, when the composition is heated and polymerized in the presence of a curing catalyst such as imidazoles, a resin can be produced. However, the document does not specifically disclose a case of using imidazoles.